Concrete Bags Calculator

How it works

The volume is converted to cubic feet (27 cu ft per cubic yard) and the waste allowance is added. Dividing by the yield of one bag and rounding up gives the bag count; the total weight is the bag count times the bag weight.

Mixing water comes from Table 2 of the QUIKRETE Concrete Mix data sheet, which gives a starting water content and a maximum expected water content for each bag size. Both are multiplied by the bag count and converted from pints to gallons (8 pints per US gallon). The data sheet's directions begin with the lower figure and add water until the mix is workable; the higher figure is the most it expects.

The data sheet allows at least 1 cu ft of mixer capacity for each 80 lb bag mixed at one time. The calculator scales that allowance by bag weight for the other sizes, divides the mixer capacity by it and rounds down for the bags per batch, then divides the bag count by that and rounds up for the number of batches.

Formula

volume (cu ft)   = volume (cu yd) × 27, or as entered in cu ft
with waste       = volume (cu ft) × (1 + waste ÷ 100)
bags             = ⌈ with waste ÷ yield per bag ⌉
water (gal)      = bags × pints per bag ÷ 8   (starting and maximum expected)
bags per batch   = ⌊ mixer capacity ÷ (1 cu ft × bag weight ÷ 80 lb) ⌋
batches          = ⌈ bags ÷ bags per batch ⌉
yield (cu ft):  40 lb 0.30 · 50 lb 0.375 · 60 lb 0.45 · 80 lb 0.60 · 90 lb 0.675
water (pt/bag): 40 lb 3–4½ · 50 lb 3½–5½ · 60 lb 4–7 · 80 lb 6–9 · 90 lb 7–10
(QUIKRETE Concrete Mix No. 1101 data sheet, rev. Oct 2022, Yield and Table 2)

Example

One cubic yard is 27 cu ft; with 10% waste that is 29.7 cu ft. In 80 lb bags at 0.60 cu ft each it is 29.7 ÷ 0.60 = 49.5, so 50 bags weighing 4,000 lb.

At 6 to 9 pints per bag the 50 bags take 300 to 450 pints of water, or 37.5 to 56.25 gallons. A 3.5 cu ft mixer holds three 80 lb bags at 1 cu ft each, so the job is 50 ÷ 3 = 16.7, rounded up to 17 batches.

Assumptions and limitations

• Bag yields are the approximate figures on the QUIKRETE Concrete Mix No. 1101 data sheet (revised October 2022): 0.30 cu ft per 40 lb bag, 0.375 per 50 lb, 0.45 per 60 lb, 0.60 per 80 lb and 0.675 per 90 lb. Other brands and mixes yield differently and the bag label governs.
• Mixing water is the starting and maximum expected range from Table 2 of the same data sheet; the actual amount depends on the aggregate moisture and the slump wanted, and the bag's own directions govern. The water is for mixing only: wetting forms, tools and curing need more.
• The data sheet gives the mixer allowance (at least 1 cu ft per bag mixed at one time) for the 80 lb bag only. Scaling it by bag weight for the other sizes is this calculator's assumption. Each batch is assumed to be whole bags; the last batch may be smaller.
• The waste allowance is a typical figure and is editable; set it to 0 if the volume you entered already includes waste.
• This is a material estimate. It is not a substitute for the manufacturer's instructions or for engineering where the concrete is structural.

Frequently asked questions